British troops deployed abroad are not protected by human rights legislation outside of military bases, the supreme court ruled today.

The majority ruling, by six of nine justices, quashed previous landmark judgments that overseas troops are also protected outside camp. The case was originally brought by the mother of Private Jason Smith, 32, who died of heatstroke while on a UK base in Iraq in 2003.

But the supreme court upheld the previous ruling that a full, fresh inquest which considers the right to life should be held into Smith's death. That decision which will open the doors to enhanced inquests which are held in cases where there is an alleged breach of the right to life under the European Convention on Human Rights.

The inquest will investigate whether the MoD had sufficient systems in place to protect soldiers from high temperatures and whether there were systemic failures which contributed to Smith's death.

His mother, Catherine, she was very disappointed by the ruling on jurisdiction but welcomed the second inquest which would mean that, after seven years, the family would have access to the medical notes into the circumstances surrounding his death.

Amid fears of costly compensation claims, the MoD had argued that the rulings could hamper difficult military decisions in conflict zones.

The supreme court was asked to decide whether a British soldier on military service in Iraq is covered by human rights laws wherever they were serving, not only when on a British military base or hospital.

Lord Phillips, the president of the supreme court, said personnel would not be covered as a matter of course. He added that it was ultimately up to the European Court of Human Rights in Strasbourg to resolve the issue.

He said: "The court has held that those who concluded the human rights convention shortly after the second world war agreed to accept obligations in relation to the way in which they treated those within their own countries.

"Only in exceptional circumstances did they agree that the convention should impose obligations on them in relation to those outside their territorial jurisdiction.

"Decisions of the European court at Strasbourg have identified those exceptional circumstances and the court has not held that they extend to servicemen abroad."

He added that three dissented members of the supreme court held that the convention does protect armed forces abroad. However, the court unanimiously agreed that even if the convention does protect those serving abroad, there was no inference that it had been breached whenever someone died on active service.

Jocelyn Cockburn, who represented Mrs Smith, said the decision on jurisdiction was shocking. "It is artificial to assert that rights can be protected on base but not off base.

"It is impossible to see how the physicality of a base (whether that be a camp in the desert or other military installation) makes any difference to the question of whether a UK soldier is subject to UK jurisdiction.

"Is the court saying that the moment a soldier steps over the line in the sand and is 'off-base' he has no 'rights'?"

She said that Mrs Smith had achieved a "significant" victory over the ruling for a fresh inquest with full disclosure.

John Wadham, group legal director at the Equality and Human Rights Commission, said: "Extending human rights protection is not about individual decisions in the heat of battle, but ensuring that when we send soldiers off to war they are properly prepared; kitted out correctly and with equipment fit for combat."

"However, we welcome the fact that Private Smith's death will now be investigated fully and that open, independent investigations will have to be held into deaths which take place in similar circumstances in the future."

In March, the MoD appealed against a court of appeal ruling that sending military personnel into battle or patrol with defective equipment could breach their human rights.

James Eadie QC, representing the MoD, had told the March hearing it would never be possible to guarantee rights under the European convention to soldiers on duty wherever they are in the world.

"The court of appeal's approach, if correct, would impose an obligation upon the UK to be able to ensure that a British soldier on duty in say a market in Kabul, Afghanistan, can enjoy convention rights without hindrance, even from those Afghans over whom the UK has no legislative or practical control and where the territory is not controlled by the UK."

Smith, 32, from Hawick, Roxburghshire, was a reservist deployed in Iraq in June 2003. He repeatedly told medical staff he was feeling unwell due to the heat – sometimes over 50C (122F) – before reporting sick in August. He was taken to hospital, but had suffered a cardiac arrest.

Andrew Walker, the assistant deputy coroner for Oxfordshire, recorded at his initial inquest in November 2006 that the soldier's death was caused "by a serious failure to recognise and take appropriate steps to address the difficulty that he had in adjusting to the climate".